1. Field of the Invention
An aspect of the present invention relates to a rotary striking tool which is driven and rotated by a motor to thereby fasten a fastening member such as a screw or a bolt by using an intermittent striking force.
2. Description of the Related Art
As a rotary striking tool (driving tool), an impact tool which fastens a screw or a bolt etc. by applying a rotation force or a rotational-direction striking force is known. JP-2005-305578-A discloses an impact driver as the kinds of the rotary striking tool. Further, there is known an oil pulse tool using an oil pulse unit as a striking mechanism. In the impact driver disclosed in JP-2005-305578-A, a hummer part rotates while being axially-movable by using a spring or a cam mechanism, and a hammer strikes an anvil once or twice with respect to a single rotation of the anvil.
The oil pulse tool has a feature that the level of the operation sound is low since metal parts never contact to each other. In the oil pulse tool, a motor is used as a power source for driving an oil pulse unit, and the rotation shaft of the motor is directly coupled to the oil pulse unit. When a trigger switch for operating the oil pulse tool is pulled, a driving electric power is supplied to the motor. The rotation speed of the motor is controlled by changing the driving force of the motor in response to the pulling amount of the trigger switch. When the oil pulse unit generates a pulse torque, a strong striking torque is transmitted to a tip tool, whereby a torque sensor detects the peak torque of the output shaft at every striking operation. An angular sensor is provided at the output shaft to detect the rotation angle of the output shaft, whereby the peak torque value is controlled to approach a target torque value in accordance with a difference between the previously-set target curve of the peak torque values from the fastening start timing to the fastening completion timing and the measured peak torque value.
In the sold oil pulse tool, an increasing amount of the rotation angle at each striking is calculated based on an angle value obtained from an angular sensor. When the increasing amount of the rotation angle is larger than a reference value (seating state determination value), it is determined that the fastening operation is not completed yet to thereby continue the striking operation even if a peak torque exceeds a reference value (fastening operation completion determination value). The motor is stopped when two conditions are satisfied that the peak value exceeds the fastening operation completion determination value and the increasing amount of the rotation angle is smaller than the seating state determination value. In order to surely control the fastening operation completion state based on the two conditions of the peak torque and the increasing amount of the rotation angle, it is necessary to provide a torque sensor and an angular sensor at the output shaft of the oil pulse tool, so that a rotary transformer is required in order to transmit and receive signals to and from these sensors. As a result, the impact tool is enlarged to provide the angular sensor and the rotary transformer etc., whereby electric wiring becomes complicated and the tool becomes expensive.